This invention relates to a vacuum-controlled vertical lifting apparatus for lifting a load. The particular embodiment disclosed in this application is an apparatus for lifting and dumping a refuse container. The lifting apparatus is typically attached to the back of a refuse collection truck. The refuse container preferably used with the lifting apparatus is a lightweight plastic container mounted on wheels and generally referred to as a "rollout" refuse container. While relatively lightweight, these containers are large and the materials from which they are constructed are inherently low in friction. Also, the containers are quite often wet from rain or snow when emptied. These factors increase the problem of shearing, in which an object being held by a vertical side tends to slip downwardly under the influence of gravity.
Prior art lifting units generally have hooks which engage bars or molded recesses in the container. The hooks are attached to an arm which lifts and inverts the container over the vehicle where the contents of the container free fall out of the container. These prior art lifting units can cause damage to the container particularly if the container is not loaded properly onto the hooks or if the vehicle is parked on a hill or uneven pavement. As the container is being lowered after emptying the bottom of the container can hit the pavement before the hooks disengage the container, damaging the lifting elements of the container.
These prior art devices are referred to as "semi-automatic" units since the container must be carefully oriented manually onto the hooks before lifting can begin. Since containers made for use on these units have lifting elements only on one side, the container must be manually rotated up to 180.degree. before moving the container into engagement with the hooks. This slows down the collection process. These disadvantages have effectively prevented the development of a completely automated lifting system wherein the container is moved into the proximity of the lifting unit without orientation of the container being required, whereupon the container is lifted.
The use of vacuum presents several desirable possibilities. In particular, since vacuum operates most effectively on a smooth, flat or regularly curved surface, a container having a simple, clean design is possible. Likewise, a vacuum pad can attach itself to many different areas of a container and can thus make precise orientation of the container unnecessary. Other problems such as unlevel or sidehill surfaces are minimized. Should the container collide with another object, the container can be knocked loose before damage is done to the container or the lifting unit. The application of both a vacuum and mechanical hold on the container reduces or eliminates the tendency of shear forces to cause the container to slide of fall from the vacuum pad.